A pendant-type sprinkler head is commonly used in commercial and industrial buildings. A sprinkler head of this type includes a cast metal frame having a base that defines an outlet connected to the water piping system. The frame is composed of a pair of arms that extend outwardly from the base and are connected together at a junction. The outlet in the base is normally enclosed by a cap, which is held in the closed position by a lever assembly that extends between the cap and the junction. A fusible link, including a fusible element or metal, retains the lever assembly in position to close off the outlet. On exposure to an elevated temperature, the fusible metal will melt, releasing the lever assembly to open the outlet to the water line.
With the increased use of sprinkler systems in hospitals, hotels, nursing homes and residences, where the prime object is to save human life, as opposed to property protection, there has been a demand for a faster response sprinkler head, meaning one that will release more quickly when exposed to elevated temperatures.
U.S. Pat. No. 4,757,865 discloses a fast response sprinkler head, in which the fusible link assembly includes a pair of thin metal discs or sheets which are joined together by a layer of fusible metal or solder. Each sheet is formed with mating open-ended recesses that define an opening which receives the lever members. The sheets are provided with bent tabs or fins which increase the frontal area exposed to the heat of combustion, thereby increasing the rate of heat transfer to the fusible link and achieving a faster response time. However, with the fast response sprinkler head as described in U.S. Pat. No. 4,757,865, the entire sprinkler head is located beneath the ceiling, in a position where it is exposed to view.
In residential dwellings, office buildings, hotels, and other commercial establishments, it is often desired to utilize a sprinkler head that is located above the ceiling, so that the operative parts are not exposed to view. U.S. Pat. Nos. 3,633,676, 3,714,989, 3,756,321 and 4,105,076 describe concealed sprinkler head installations, where the sprinkler head is concealed within the ceiling by a decorative plate that is mounted flush against the ceiling, so that none of the operative parts are visible.